The present disclosure is related to air filtering systems for removing particulate and chemical contaminants from intake air. In particular, the disclosure is directed to a filter assembly that removes particulate and chemical contaminants from the intake air of fuel cells, and that also provides sound attenuation.
Practical and efficient generation of electrical energy has been sought since the discovery of electricity. Hydroelectric, fossil fuel and nuclear generation plants and batteries have long been used to supply our electrical power needs. Power generation by use of fuel cells is a relatively recent development that is rapidly gaining acceptance for both commercial and residential applications. As compared with conventional fossil fuel burning powered sources, they are relatively clean and efficient. Fuel cells are electrochemical devices that efficiently convert a fuel""s chemical energy directly to electrical energy. They chemically combine a fuel and oxidant without burning, thereby eliminating many inefficiencies and most pollution of traditional combustion power systems.
A fuel cell operates in principle much like a battery. However, unlike a battery, a fuel cell does not run down or require recharging. It will continue to produce energy in the form of electricity and heat as long as fuel is supplied to it. In general, a fuel cell consists of two electrodes (an anode and a cathode) sandwiched around an electrolyte. For example, for a PEM fuel cell, hydrogen and oxygen are passed over the anode and cathode electrodes respectively in a manner that generates a voltage between the electrodes, creating electricity and heat, and producing water as the primary byproduct. The hydrogen fuel is supplied to the anode of the fuel cell. Some consume hydrogen directly, while others use a fuel reformer to extract the hydrogen from, for example, a hydrocarbon fuel such as natural gas, methanol, ethanol, or gasoline. Oxygen enters the fuel cell at the cathode. The oxygen can be supplied in purified form or can come directly from atmospheric air.
The fuel cell uses a catalyst to cause the hydrogen atom to split into a proton and an electron, each of which takes a different path to the cathode. The protons pass through the electrolyte. The electrons create a useful electric current that can be used as an energy source, before returning to the anode where they are reunited with the hydrogen protons and the oxygen to form water.
Fuel cells are generally characterized by the electrolyte material which is sandwiched between the cathode and anode, and which serves as a bridge for ion exchange. There are five main known types of fuel cells. Alkaline fuel cells (AFCs) contain a liquid alkaline electrolyte and have been used primarily in space mission applications. Proton exchange membrane fuel cells (PEMFCs) contain a solid polymer electrolyte. Their low temperature operation, high power density with the ability to vary their output quickly to meet shifts in power demand make their use ideal for both mobile and stationary applications, such as powering vehicles or buildings. Phosphoric acid fuel cells (PAFCs) utilize a phosphoric acid electrolyte and are currently used for commercial power generation. Molten carbonate fuel cells (MCFCs) contain a carbonate salt electrolyte, which becomes molten at the operating temperature of about 650xc2x0 C. Solid oxide fuel cells (SOFCs) use a ceramic electrolyte material and operate up to about 1000xc2x0 C. Both the MCFCs and the SOFCs can use carbon monoxide as fuel.
Fuel cells have a vast range of potential applications. They can be used to produce electricity for homes, businesses and industries through stationary power plants. Fuel cells produce a direct current (dc) that must be inverted to alternating current for grid-connected applications or for use with most consumer products. However, future fuel cells could be operated in both grid-connected and non-grid-connected modes. For residential applications, smaller fuel cell power plants could be installed for the production of both heat and power. They could also be used to provide power to remote residential entities having no access to primary grid power, potentially eliminating the necessity of grid-connections.
In addition to the larger scale power production applications, fuel cells could replace batteries that power consumer electronic products such as laptop computers, cellular phones and the like and could even be micro-machined to provide power directly to computer chips. Another promising commercial application of fuel cells is their potential to replace the internal combustion engine in vehicle and transportation applications. The applications for fuel cells are virtually unlimited.
All of the known fuel cell configurations discussed above have a common need for oxygen as an integral ingredient for performing the cell""s chemical process. Other power sources, such as internal combustion engines, including diesel engines, also have a need for oxygen. For most commercial applications it is desirable for such oxygen to be supplied directly from the atmospheric air. However, it is accepted that in today""s world, all atmospheric air has some degree of contaminants present in it. Such contaminants can be relatively large such as loose debris, insects, tree blossoms or the like, or can be in the nature of small particulates suspended in the atmosphere such as dust, tree pollen, smog or smoke particulates. Chemical contaminants are also widely present in atmospheric air, whether as a result of man-made pollution or as those which naturally occur. Typical chemical contaminants might include volatile organic compounds such as aromatic hydrocarbons, methane, butane, propane and other hydrocarbons as well as ammonia, oxides of nitrogen, ozone, smog, oxides of sulfur, carbon monoxide, hydrogen sulfide, etc. Such contaminants may appear intentionally (such as in military environments or by terrorists) or unintentionally. Solution of the latter requirement becomes particularly acute when the fuel cell is used in a mobile application that subjects the fuel cell to many varied atmospheric conditions.
Since efficient fuel cell operation depends on a delicately balanced chemical reaction, contaminants in the air used by the cell can have a significant adverse effect on the cell""s operation and, depending on their nature, can even cause the fuel cell to discontinue operation. It is important therefore, that the fuel cell system include a filtration system that is designed to eliminate harmful contaminants and one that enables the fuel cell to be used in a wide range of use environments. It is also important that other power generating equipment have a filtration system that is designed to eliminate harmful contaminants.
To obtain the amount of oxygen necessary for a fuel cell and other equipment to produce the desired energy output, it has been found desirable to pass the oxygen-bearing containing air through air movement equipment such as a compressor or fan located within the air flow stream supplied to the fuel cell or other equipment. Unfortunately, typical compressors produce significant undesirable and annoying noise levels. It is desirable, therefore, in a power generating system to reduce and to minimize the noise produced by and/or transmitted through the compressor and back into the environment. Since reduced system size is also typically desirable, it is preferable that the filtration and sound attenuation features of the system be physically reduced as small as possible and even preferably be combined within a single element or housing. The present invention addresses the above-identified needs and desires for an efficient and quiet system for use in a wide variety of applications, including fuel cell systems.
What is desired, therefore, is a power generator, such as a fuel cell, that functions within environments having a wide range of contaminants.
The present invention provides filter assemblies for filtering the intake air used in power generating systems, such as with fuel cells. The present invention addresses a number of issues associated with the practical implementation of fuel cell technology for power generation, whether that application is for generation of power in large stationary applications, vehicles, mobile lightweight equipment such as laptop computers or cell phones, or small stationary equipment such as radar detectors or sensors. These applications may draw less than 1 kW of power, or up to several megawatts of power. The filter assemblies of the present invention address the common need of generally all such applications, that is the need for a contaminant free supply of oxidant to the fuel cell, or at least a supply of oxidant having a reduced contaminant level.
The amount and types of contaminants desirous to be removed from the intake air will depend on the amount and types of contaminants initially present in the intake air (generally, the atmosphere or environment surrounding the fuel cell). The amount of contaminants and the type of contaminants present in the intake stream, prior to filtration, varies widely depending on the location of the fuel cell, or at least the location of the air intake. For example, some environments have large levels of particulate contamination such as dust, smog, smoke, or pollen, whereas other environments having large levels of chemical contaminants such as ammonia, carbon monoxide, sulfur dioxide, or silicone. Generally, no two environments will have identical contaminant profiles.
The amount and types of contaminants desirous to be removed from the intake air will also depend on the type of fuel cell. Any type of fuel cell or fuel cell stack can be used with the filter assemblies of the present invention, such as, for example, PEM fuel cells, solid oxide fuel cells, phosphoric acid fuel cells, and molten carbonate fuel cells. Typically, the higher temperature operating fuel cells, such as solid oxide fuel cells, can tolerate higher levels of organic contaminants than lower temperature operating fuel cells, such as PEM fuel cells.
Accordingly, one aspect of this invention is to provide filtration to the intake air for a fuel cell system. The assemblies of the present invention provide particulate filtration and/or chemical filtration to the incoming air stream to provide a purified oxidant supply. Since most fuel cell system include some type of air moving equipment, such as a compressor, which can introduce contaminants into the air stream, the present invention also addresses filtration of air downstream of the air moving equipment.
Unfortunately, air moving equipment typically produces loud noise in exchange for its air moving capabilities. It is the moving parts such as rotors, impellers, lobes, vanes, pistons and other various parts of air moving equipment that create sound waves or noise in the frequency ranges of 3 Hertz to 30,000 Hertz, sometimes as high as 50,000 Hertz, at levels of 85 to 135 db at one meter. While not all the noise emanating from the air moving equipment is objectionable, the various assemblies of the present invention are directed to reducing the most objectionable portions of the noise profiles.
In one particular embodiment, the invention is directed to a system for producing power. The system comprises an air filter assembly that comprises a housing and a filter element in the housing. The housing has an inlet and an outlet, the inlet accepting dirty atmospheric air to the filter assembly, and the outlet providing clean air from the filter assembly. The filter element comprises at least a physical or particulate filter portion to remove particulate contaminants from the dirty air. The filter element may also include a chemical filter portion to remove chemical contaminants from the dirty air. The filter assembly also includes a sound suppression or attenuation element, which may also be in the housing. The sound suppression element provides broadband attenuation of the sound passing through the filter assembly. The air filter assembly is operably connected to a power generation source, such as a fuel cell.
The system generally also includes air moving equipment, such as a compressor or a blower, to provide enhanced air flow to the fuel cell. The filter assembly is also particularly arranged to reduce the level of noise emanating from any such equipment.
The present invention provides a filter assembly, the filter assembly having a housing and a filter element in the housing. The housing has an inlet and an outlet, the inlet receiving dirty air into the filter assembly, and the outlet providing clean filtered air from the filter assembly. The filter assembly generally also has a sound suppression element, such as a resonator, sonic choke, full choke, sound adsorbent material, that attenuates or otherwise reduces sound passing through the housing by at least 3 db at one meter, preferably by at least 6 db.
The filter element can include a particulate filter portion, a chemical filter portion, and optionally a sound suppression element, all being part of the filter element. The sound suppression element provides broadband sound attenuation of at least 6 db at one meter. The particulate filter portion removes particulate contaminants from dirty air entering the filter element, and the chemical filter portion, if present, is removes chemical contaminants from the entering dirty air. The particulate filter portion can be positioned radially adjacent or forming a part of the sound suppression element. In some configurations, the particulate filter portion can be configured to provide straight-through flow.
Such a filter assembly or filter element can be used with any process or system that produces noise or sound and that benefits from cleaner intake gas (such as air). A fuel cell system is one power producing system with which filter assembly of the present invention can be used. Additionally, the filter assembly or filter element can be used with other power producing systems, such as diesel or gasoline engines.